The overall objective of this proposal is to develop hepatitis C virus (HCV)-specific immunogens that may be useful as prophylactic and/or therapeutic vaccines for the prevention or treatment of chronic HCV infection. Two general nonexclusive approaches are proposed. In the first approach (Specific Aim 1) we propose to develop a prophylactic HCV vaccine designed to elicit neutralizing antibodies to the HCV E2 protein. For this purpose we have developed the woodchuck hepatitis core protein (WHcAg) as a particulate vaccine carrier platform. The WHcAg platform is capable of accommodating a variety of inserted B cell and CD4 + T cell epitopes and elicits extremely high levels of antibodies to the inserted B cell epitopes and primes insert-specific CD4 v T cells. Three categories of E2-specific neutralizing B cell epitopes will be inserted into the WHcAg vaccine platform: (a) highly conserved, non-HVR1 E2 epitopes that we have identified; (b) consensus sequences derived from the highly variable HVR1 region of E2, which will address the problem of genetic variability of HCV; and (c) conserved "framework motifs" present within the HVR1 region. The E2- WHcAg hybrid particles will be optimized for protein expression, assembly competence, yield in the E. coil expression system, antigenicity and immunogenicity. Because strong T cell responses (both CD4 vand CD8 v) against HCV antigens and especially the nonstructural 3 (NS3) protein have been linked to viral clearance in acute and chronic HCV infection, our second approach will be aimed at developing a NS3/4A-specific DNA vaccine candidate (Specific Aim 2). The NS3 protein is highly conserved and an advantage of a DNA vaccine is the ability to elicit CD4 v Th cells and CD8 v CTL as well as antibody. We have found that a NS3/4A gene elicits significantly more efficient immune responses than the widely used NS3 gene. It is anticipated that a NS3/4A DNA vaccine may be used for prophylactic or therapeutic applications either alone or in combination with E2-WHcAg hybrid particles.